you should take a look at youtube channel, he covers what you need to do to create a vehicle in blender that’s ready for use in UE4 and how to set things up in both blender and UE4. kenny is right in that you don’t need leaf bones, they just add extra bones that don’t do anything. also you don’t actually need to set up constraints for the wheels in UE4, I had a car that would spas out in the physics editor but it worked fine when playing.
hope that helps:)
its true that you can import a vehicle without bones and UE4 will create them but that only really works well for very basic vehicles, if you want to make a more complicated vehicle with say moving suspension like this:
then its much easier and quicker to use bones.